Biological control agents in plant disease control - Disease Control in Crops - page 35

methods, including air- and freeze-drying, drying on silica gel and spray- and fl uid
bed-drying. These methods reduce the metabolic rate of the inoculum by removing the
available water, which tends to preserve the inoculum with high viability depending on
the BCA. Once the inoculum is dried, it is usually mixed with various components such
as carriers, bulking agents, diluents and food bases. BCAs have been formulated as dusts,
gels, emulsions, prills, pellets and granules for seed treatments, dips, wettable powders
and sprays for application to aerial plant parts, and drenches for incorporation into soil
and growing media (Fravel et al ., 1998). Most work on formulation closely involves agro-
chemical, biotechnology or seed-treatment companies and, unfortunately, tends not to be
published. The fi nal formulated product should be convenient to use, safe to handle and
have an adequate shelf life with stability for at least 1 year. Other desirable characteristics
of a formulation include compatibility with application machinery, and ease of integration
into integrated pest and disease control systems.
Both quality assurance and technical support are important to ensure that the formu-
lated product contains the appropriate active BCA without contamination, and is applied
correctly to ensure effi cacy. Quality assurance and extensive technical support have been
instrumental in the success of Serenade, a product containing the bacterium Bacillus sub-
tilis , and used to reduce post-harvest diseases of citrus and pome fruit (Janisiewicz &
Korsten, 2002). The success of products based on Bacillus (Tables 3.1 and 3.2) is largely
related to their ability to form spores and their ease of formulation and storage (Schisler
et al ., 2004).
Large-scale fi eld application of BCAs poses practical problems in terms of producing
suffi cient amounts required to reach the target plant pathogen, and achieve effi cacy, as
well as concerns over production costs. The target and timing of application depends on
the BCA, the pathogen and also the crop. There has been extensive research directed at
improving the application and performance of BCAs, and reducing the amounts required
for control. One way of reducing the amount of BCA required to control both seed and
soil-borne diseases is to apply the agent to seed rather than in-furrow, or as a soil or grow-
ing medium incorporation (McQuilken et al ., 1998). Application of BCAs to seed has the
potential to deliver the agent 'in the right amount, at the right place and at the right time'.
However, the process of applying BCAs to seeds presents a special set of technical con-
siderations. For example, suffi cient numbers of the BCA must survive the process, and be
able to grow and colonise the environment of the germinating seed fast enough to provide
control. The BCA must also be able to survive a period of low water activity as the seed
has to be stored at low moisture levels. Colonisation of seeds by BCAs during germina-
tion can be improved by incorporating the agent during seed priming, a process used for
the physiological enhancement of germination (McQuilken et al ., 1998). This has been
done successfully for Trichoderma spp. applied through solid matrix priming (Harman,
1991), and recently in the United Kingdom through drum priming for several bacterial
species, including Bacillus subtilis and Pseudomonas fl uorescens (Wright et al ., 2003).
The use of drum priming is a major advance in the application of BCAs to seeds and has
signifi cant commercial potential.
There has been considerable interest in the use of insects to apply and disseminate
BCAs to aerial microbiomes. For example, honey and bumble bees have been used suc-
cessfully to spread both bacterial and fungal BCAs to specifi c sites such as soft and
pome fruit fl owers to control diseases including grey mould and fi reblight, caused by